It appears, most maintainers only have been ignoring the description
fields or not filling them properly because of lack of documentation or
awareness on how it is being used.

Some of the replies in these threads don't quite suggest that. People
complain about the "bureaucracy" of being "forced" to write such stuff,
which pretty much shows they intentionally do not want to fill in those
fields and won't do it if they can get away without it.

Not quite, I fill %changelog with with what I consider to be reasonable
in a particular situation.